1. Field of the Invention
The present invention relates to a printing plate printer for printing an image recorded on an original film onto a printing plate, and more particularly to an original film holder for holding the original film in position with respect to the printing plate, especially a lithographic printing plate. In addition, the present invention relates to a reference pin for positioning a printing plate used for a printing plate printer for positioning the printing plate by coming into contact with an end face of the printing plate, and also concerns a pusher for positioning the printing plate by pushing and moving the printing plate.
2. Description of the Related Art
A printing plate printer prints an image recorded on an original film onto a lithographic printing plate such as a presensitized plate. In the printing plate printer, after the lithographic printing plate (hereinafter referred to as a PS plate) is placed at a predetermined position on a printing surface plate opposing a light source, an original film is placed at a predetermined position on an upper surface of the PS plate, and light from the light source is radiated to the PS plate via the original film. The image on the original film is hereby printed onto the PS plate.
The PS plate is positioned with respect to the printing surface plate in a state in which the PS plate is placed on the printing surface plate. As a method for positioning the PS plate on the printing surface plate, a method is known in which the PS plate is pushed and moved by a pusher toward a positioning pin disposed at a predetermined position so as to be brought into contact with the positioning pin. In this method of positioning the PS plate, since the PS plate is moved by being slid on the printing surface plate, the positioning pin and the pusher are disposed in such a manner as to project upward and retract downward from the upper surface of the printing surface plate. In the state in which the positioning pin and the pusher are accommodated below the printing surface plate, these members are so arranged as not to interfere with the movement of the PS plate on the printing surface plate.
As the pusher disposed in such a manner as to project upward and retract downward from the upper surface of the printing surface plate, a pusher is known in which a pushing portion thereof for coming into contact with the PS plate is accommodated in an inclined manner in an elongated hole provided in the printing surface plate. A distal end portion of this pusher is made to project upward from the elongated hole as its pushing portion is raised diagonally upward. The pusher is then moved along the elongated hole in this projected state so as to push the opposing PS plate.
In addition, the positioning pin is disposed at a distal end of a rod which is moved vertically as a cylinder, for instance, is driven. In this state in which this positioning pin projects upward, as an end face of the PS plate is brought into contact with an outer peripheral surface of this pin, the PS plate is positioned.
With the above-described pusher, since the pushing portion is accommodated in the elongated hole by being inclined, a portion of the elongated hole is used as a rotating space for accommodating the pushing portion and causing the pushing portion to project therefrom. Hence, the range of movement of the pushing portion is narrow despite the length of the elongated hole. For this reason, in order to reliably push and move the PS plate, it is necessary to provide an elongated hole having a length more than is necessary on the printing surface plate.
In addition, as for the positioning pin, it is necessary for its projecting position not to move, but in the event that the rod has rotated and its axial position has been offset, the position of the positioning pin also becomes offset, thereby making it impossible to position the PS plate accurately in some cases.
Also, a printing plate printer is known which is provided with a film holder in which pins are disposed uprightly on the printing surface plate or adjacent to the printing surface plate. This film holder is adapted to hold a negative film by inserting pins through punch holes formed in advance at predetermined positions of the negative film, whereby an image portion of the negative film can be arranged at a predetermined position on the printing surface plate.
fin such a film holder, as a method of inserting the pins through the punch holes in the negative film, the negative film is first arranged such that the punch holes are positioned above the pins, and the pins are then moved vertically and inserted through the punch holes so as to hold the negative film. In this method, when the holding of the negative film is canceled, the pins are moved downwardly and drawn out of the punch holes so as to remove the negative film.
As another method of inserting the pins through the punch holes, a method is known in which the film is first sucked and held by a film sucking means, and the film sucking means is then lowered to allow the punch holes provided in the negative film to be fitted over the pins disposed uprightly on the film holder to hold the negative film. After printing, the negative film is raised by the sucking means so as to remove the negative film from the pins.
However, with the former method in which only the pins are vertically moved to be inserted through or removed from the punch holes in the negative film, there are cases where the axes of the pins themselves are offset. Consequently, it sometimes becomes impossible for the pins to be accurately inserted through the punch holes in the negative film and for an image portion of the negative film to be arranged at a predetermined position on the PS plate.
In addition, with the latter method, there are problems in that a punch hole portion of the negative film can be caught by the pin, which makes it impossible for the negative film to be removed, and that the punch hole becomes damaged at the time when the negative film is held by suckers, the punch holes in the negative film are fitted over the pins disposed uprightly on the film holder, and after the printing of the image on the negative film onto the PS plate, the negative film is lifted up by the suckers and is removed from the film holder.
Furthermore, in a case where an identical image is printed on a plurality of PS plates, since only the PS plate is moved and positioned with the original film superposed on the PS plate, there are cases where the original film is also moved and becomes twisted during that movement, thereby making it impossible to maintain a proper position.